Non-linear transition shift identification and compensation

ABSTRACT

A system for identifying and compensating for non-linear transition shift in a magnetic medium data storage device is disclosed. The non-linear transition shift compensation system includes a non-linear transition shift estimation module adapted to generate non-linear transition shift estimates for specific bit patterns. The system further includes a pre-compensation module adapted to adjust the temporal spacing of binary transitions written to the magnetic medium based on the non-linear transition shift estimates generated by the non-linear transition shift estimation module for specific bit patterns corresponding to bit patterns appearing in the data being written to the magnetic medium.

RELATED APPLICATIONS

This application is a divisional application of U.S. Non-Provisionalapplication Ser. No. 11/784,482, filed Apr. 6, 2007 (now U.S. Pat. No.7,974,032), which claims the benefit of U.S. Provisional Application No.60/790,877, filed Apr. 11, 2006, and U.S. Provisional Application No.60/883,871, filed Jan. 8, 2007. The contents of U.S. Non-Provisionalapplication Ser. No. 11/784,482 (now U.S. Pat. No. 7,974,032), U.S.Provisional Application No. 60/790,877, and U.S. Provisional ApplicationNo. 60/883,871 are hereby incorporated by reference in their entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to magnetic media data storage devices.More particularly, the disclosure relates to a system and method foridentifying and compensating for non-linear transition shift in magneticmedia data storage devices.

2. Related Art

Non-linear transition shift is a phenomenon that affects the timing ofthe binary transitions of data signals written to the magnetic media inmagnetic media data storage devices. When the recording head of amagnetic media data storage device attempts to write a binary transitionto the recording medium, the current transition is affected by themagnetic fields of previously written transitions. These magnetic fieldscan cause the current transition to be shifted in time such that thetransition is written either earlier or later than intended. Such timeshifts can be a source of noise leading to unacceptable bit error rateswhen data stored on the magnetic medium are subsequently read back andused by associated data processing equipment.

If the amount of non-linear transition shift affecting a particularbinary transition is known in advance, it is possible to compensate forthe shift when the transition is written to the magnetic recordingmedium. For example, if it is known that a particular transition will bedelayed by 0.1 nanoseconds, it is possible to write the transition 0.1nanoseconds earlier. When the timing of a transition is pre-compensatedin this manner, the transition will occur precisely where intended whenit is subsequently read from the recording medium. A problem, however,is that non-linear transition is inconsistent. The magnetic fields thatcause non-linear transition shift depend on the sequence of bits near aparticular binary transition. Thus, the amount and direction ofnon-linear transition shift experienced by a particular binarytransition will be dependent on the particular data sequence beingwritten to the magnetic storage medium.

A traditional approach to compensating for non-linear transition shiftinvolves generating a pseudorandom sequence of binary data, writing thepseudorandom sequence to the magnetic recording medium, and reading itback. The recovered sequence is then analyzed to determine the effectthat the various bit patterns in the pseudorandom sequence have had onthe corresponding binary transitions recorded on the magnetic medium.This traditional approach suffers from a number of drawbacks. The maindrawbacks of this approach are that it typically requires over-samplingof the waveforms, it is not very accurate, and only a limited number ofdata patterns may be specified for defining the associated NLTS values.Furthermore, the compensation values may not be refined over time underactual operating conditions. An improved approach is desirable.

BRIEF SUMMARY

The following embodiments relate to systems and methods of identifyingand compensating for non-linear transition shift in binary transitionswritten to magnetic media data storage devices. It is noted thatthroughout the specification the term “data” may relate to a datacarrying waveform (e.g., an analog signal carrying binary transitioninformation) or a binary sequence of bits, depending on the component inthe pipeline being discussed.

In the embodiments described below, non-linear transition shift ismeasured “on-the-fly” and non-linear transition shift pre-compensationvalues are continuously updated to ensure that the most accurate andup-to-date pre-compensation values are employed when writing data (ananalog waveform transition) to the magnetic storage medium.

In one embodiment a system for identifying non-linear transition shiftof a transition in a waveform is disclosed. The system includes a bitpattern identification module adapted to identify bit patterns insegments of a data sequence read from the magnetic storage medium. Anon-linear transition shift value register bank stores a non-lineartransition shift value for each bit pattern. Each non-linear transitionshift value is either an estimate value or a fixed value. The non-lineartransition shift estimate values are updatable by an algorithmimplemented in the system. The non-linear transition shift fixed valuesare predetermined and unchangeable. The non-linear transition shiftfixed values may be based upon one or more known characteristics ofnon-linear transition shift behavior. The various non-linear transitionshift values stored in the non-linear transition shift value registerbank are associated with specific bit patterns of finite length.Finally, the system includes a non-linear transition shift errorestimation module for calculating a non-linear transition shift errorestimate based on the non-linear transition shift values stored in thenon-linear transition shift value register bank.

In another embodiment a magnetic media data storage device is disclosed.The magnetic media data storage device includes a magnetic medium and amagnetic read/write head for reading data from and writing data to themagnetic medium. A write channel prepares binary data to be written tothe magnetic medium via the magnetic write head. A magnetic head/mediachannel generates a continuous-time analog waveform that corresponds tothe data that was previously written to the magnetic medium, althoughthe magnetic head/media channel (output) waveform may be corrupted bysome noise. The magnetic media data storage device includes a non-lineartransition shift identification module adapted to identify thenon-linear transition shift of binary transitions (introduced during thewrite operation) in the waveform received from the magnetic head/mediachannel. A non-linear transition shift compensation module is adapted totemporally adjust when the binary transitions associated with specificbit patterns are written to the magnetic head/media channel. Theadjusted timing of writing a binary transition to the magnetichead/media channel may be based on the actual non-linear transitionshift identified by the non-linear transition shift identificationmodule for a specific bit pattern.

In another embodiment a system for compensating for non-lineartransition shift in a magnetic medium data storage device is disclosed.In this embodiment a non-linear transition shift compensation systemincludes a non-linear transition shift estimation module adapted togenerate non-linear transition shift estimates for specific bitpatterns. The system further includes a pre-compensation module adaptedto adjust the temporal spacing of binary transitions written to themagnetic head/media channel. The amount of pre-compensation applied to atransition is based on a non-linear transition shift estimate generatedby the non-linear transition shift estimation module. The non-lineartransition shift estimate selected as a pre-compensation value dependson the specific bit pattern associated with the transition. Preferably,at least one bit pattern is associated with a non-linear transitionshift value that is fixed, and therefore unchangeable by the non-lineartransition shift estimation module.

A method of compensating for non-linear transition shift in a binarytransition written to a magnetic data recording medium is also provided.The method includes defining a binary segment length. According to themethod, non-linear transition shift values are provided for the variousbit patterns that may be found in a binary segment of the defined binarysegment length. Each non-linear transition shift value is either anestimate value or a fixed value. Binary data are read from the magneticrecording medium. The bit patterns in segments of the binary data readfrom the magnetic medium are identified. The non-linear transitionshifts associated with binary transitions read from the magnetic mediumis determined, and the corresponding bit pattern associated with eachnon-linear transition shift is identified. The actual non-lineartransition shifts and their associated bit patterns are compared to thenon-linear transition shift estimates generated for the correspondingbit patterns. The non-linear transition shift estimate values areadjusted based on the comparison. The time at which a binary transitionassociated with a particular bit pattern is written to the magnetichead/media channel is adjusted based on the non-linear transition shiftestimates. The preferred embodiments will now be described withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a magnetic medium data storagedevice.

FIG. 2 is a flowchart illustrating a method of identifying non-lineartransition shift in a data sequence read from a magnetic storage medium.

FIG. 3 is a continuous-time plot of the magnetic head/media channel stepresponse of an ideal binary transition and a binary transition subjectto non-linear transition shift.

FIG. 4 is a continuous-time plot of the equalized target step responseof an ideal binary transition and a binary transition subject tonon-linear transition shift.

FIG. 5 is a continuous-time plot of the differentiated target stepresponse shown in FIG. 4.

FIG. 6 is a discrete-time plot of the differentiated target stepresponse shown in FIG. 4.

FIG. 7 is a table showing an example of non-linear transition shiftvalues for all of the possible bit patterns of a 4-bit segment of abinary sequence.

FIG. 8 is a representative portion of a binary sequence.

FIG. 9 is a discrete time plot of the differentiated target stepresponse of a binary transition occurring at a time k.

FIG. 10 is a discrete time plot of the differentiated target stepresponse of a binary transition occurring at a time k−1.

FIG. 11 is a discrete time plot of the differentiated target stepresponse of a binary transition occurring at a time k+1.

FIG. 12 is a block diagram of the read channel, including the read/writehead, of a magnetic medium data storage device.

FIG. 13A is a functional block diagram of a hard disk drive;

FIG. 13B is a functional block diagram of a digital versatile disk(DVD);

FIG. 13C is a functional block diagram of a high definition television;

FIG. 13D is a functional block diagram of a vehicle control system;

FIG. 13E is a functional block diagram of a cellular phone;

FIG. 13F is a functional block diagram of a set top box; and

FIG. 13G is a functional block diagram of a media player.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

The embodiments below relate to identifying non-linear transition shift(NLTS) that may occur when a binary transition is written to a magneticdata storage medium. The NLTS is identified in the read channel of aread/write magnetic data storage device and applied to data in the writechannel of the device to pre-compensate for anticipated NLTS.

FIG. 1 is a simplified block diagram of a magnetic media data storagedevice 10 including NLTS identification and compensation. The magneticdata storage device 10 includes a write channel 12, a magneticread/write head 16, a storage medium 18, and a read channel 20. Themagnetic read/write head 16 may include a separate read head and aseparate write head, or the two may be combined into a single read/writehead as shown. The magnetic read/write head 16 and the storage medium 18may be referred to in combination as a magnetic head/media channel 14.

The write channel 12 is adapted to receive user data in the form ofinput binary sequences 22 to be written to the magnetic read/write head16 and stored on the storage medium 18. The read channel 20 receives awaveform from the magnetic head/media channel 14 corresponding to dataretrieved from the storage medium 18 and outputs binary sequences 24.

The read channel 20 includes an NLTS identification block 28. The NLTSidentification block 28 identifies NLTS in the waveform received fromthe magnetic head/media channel 14. Similarly, the write channel 12includes an NLTS pre-compensation block 26. The information obtained bythe NLTS identification block 28 may be provided to the NLTSpre-compensation block 26 so that the effects of NLTS may be reduced oreliminated by delaying or advancing the individual binary transitionswritten to the magnetic head/media channel 14.

Both the read channel NLTS identification block 28 and the write channelpre-compensation block 26 may include a processor 27, e.g. a centralprocessing unit (CPU), and a memory 29, or have access to a processor 27and memory 29. The memory 29 may be configured to store instructionsthat may be executed by the processor 27 for executing the NLTSidentification and pre-compensation algorithms described below. Thememory 29 may also be adapted to store parameters and variable dataassociated with identifying and compensating for NLTS. Both the NLTSpre-compensation block 26 and the NLTS identification block 28 mayemploy their own processor 27 and memory 29, or they may share a commonprocessor 27 and memory 29. Alternatively, one or both of the NLTSidentification block 28 and the pre-compensation block 26 may access aremote processor 27 and memory 29. In alternative embodiments, dedicatedhardware implementations, such as application specific integratedcircuits, programmable logic arrays and other hardware devices, may beconstructed to implement one or more of the NLTS identification andcompensation algorithms described herein. Accordingly, the presentsystem encompasses software, firmware, and hardware implementations or acombination thereof.

NLTS is bit pattern specific. The amount and direction of NLTS for aparticular transition depends on the sequence of bits near thetransition. The NLTS identification block 28 identifies the amount anddirection of NLTS associated with individual transitions and theparticular bit patterns near them. The NLTS pre-compensation block 26adjusts the timing of a transition written to the magnetic head/mediachannel 14 by an amount and in a direction necessary to compensate foranticipated NLTS based on the bit pattern of the binary sequence nearthe transition. The pre-compensation combines with the actual NLTS suchthat NLTS error is substantially reduced or eliminated.

The NLTS identification block 28 employs an algorithm for identifyingNLTS “on-the-fly” as a waveform is received from the magnetic head/mediachannel 14. FIG. 2 is a flowchart outlining the NLTS identificationprocess. A first preliminary step 30 is to define the target (ideal)step response for the magnetic head/media channel 14. FIG. 3 shows thecontinuous-time step response 60 for an ideal binary transitionoccurring at time 0. FIG. 3 also shows the continuous-time step response62 for a binary transition subject to an NLTS. The continuous-time NLTSstep response 62 is substantially identical to the continuous-time idealstep response 60, but translated in time by an amount τ. For aparticular transition, the pattern of bits near the transition willdetermine the magnitude and direction of the NLTS shift τ.

Typically the read channel 20 of a magnetic data storage device willequalize the data signal received from the magnetic head/media channel14 so that the magnetic head/media channel 14 transfer function willconform to a desired target polynomial. FIG. 4 shows the equalizedcontinuous-time step response 64 for the continuous-time ideal stepresponse 60, and the equalized continuous-time step response 66 for thecontinuous-time NLTS step response 62. Again, the equalizedcontinuous-time NLTS step response 66 has substantially the same shapeas the equalized continuous-time ideal step response 64 but istranslated in time by the amount τ.

The equalized continuous-time ideal step response 64 may be representedas a function TS(t). The equalized continuous-time NLTS step response 66may be represented by the function TS(t+τ). The difference between theequalized continuous-time ideal step response 64 and the equalizedcontinuous-time NLTS step response 66 may be determined by the equationDTS(t)=TS(t+τ)−TS(t)  [1]For sufficiently small values of τ the difference DTS(t) may beapproximated as

$\begin{matrix}{{{{{DTS}(t)} \approx {\frac{\mathbb{d}{Ts}}{\mathbb{d}t} \cdot \tau}} = {{dts}(t)}},\mspace{14mu}{{{where}\mspace{14mu}{{dts}(t)}} = \frac{\mathbb{d}{{TS}(t)}}{\mathbb{d}t}}} & \lbrack 2\rbrack\end{matrix}$The term dts(t) is simply the time derivative of the equalizedcontinuous-time ideal step response 64 of a transition at time 0 (thetarget response). Equation [2] says that, for small valves of τ, thedifference between the equalized continuous-time NLTS step response 66and the equalized continuous-time ideal step response 64, the errorintroduced by the NLTS shift, is approximately equal to the timederivative of the equalized continuous-time ideal step response 64multiplied by the amount of the shift. This relationship is employed bythe NLTS identification algorithm in the NLTS identification block 28 toestimate the NLTS error in the waveform received from the magnetichead/media channel 14.

The next step in the NLTS identification process calls for generatingthe discrete-time differential ideal step response 32. Thecontinuous-time differential ideal step response dts(t) is not dependenton the sequence of bits read from the head/media channel 14 and may becalculated directly from the equalized continuous-time ideal stepresponse 64 (TS(t)). FIG. 5 shows the continuous time differentiation 68of the equalized continuous-time ideal step response 64 of FIG. 4. Thediscrete-time differentiation of the ideal step response may be obtainedby sampling the continuous time differentiation 68 at regular intervalsover a predefined window of time. FIG. 6 shows the discrete-timedifferentiation 70 of the equalized continuous-time ideal step response64 of FIG. 4. The discrete-time differentiation 70 comprises a pluralityof discrete data points 72 corresponding to the values of thecontinuous-time differentiation 68 of the equalized continuous-timeideal step response 64 at specific instances of time.

As has been mentioned, NLTS is determined by the specific bit pattern ofthe binary sequence in the vicinity of a particular binary transition.The influence a particular bit has on a specific transition diminisheswith its physical and temporal distance from the transition. In otherwords, those bits within a binary sequence that are nearest a transitionwill have the greatest impact on any NLTS shift experienced by thetransition. Those bits further away from the transition will have lessimpact. At some point, the impact of bits further away from a transitionbecome negligible. Accordingly, another preliminary step in the NLTSidentification process is to define the length of a binary sequencesegment 34 that will be considered when identifying and compensating forNLTS. As will be described in more detail below, a parameter d may bedefined such that a bit sequence d+1 bits long will be considered foridentifying and compensating for NLTS. In most cases a value of d in therange of 3-5 will be appropriate, although other values may be appliedas well.

The length of the binary sequence defined by the parameter d determinesthe resolution of the NLTS identification process. Because the amount ofNLTS shift experienced by a binary transition is dependent on thepattern of the waveform in the vicinity of the transition, the number ofNLTS gradations that may be identified is determined by the number ofbits in the binary sequence whose impact is considered on NLTS. Considera situation where a two bit segment of a binary sequence is employed foridentifying NLTS. This is another way of saying that the total amount ofNLTS shift experienced by a binary transition is determined by a two bitsegment of a binary sequence. A two bit segment can generate fourdistinct bit patterns:

-   -   00    -   01    -   10    -   11        Because NLTS is dependent on the bit pattern near a binary        transition, any amount of NLTS shift experienced by a binary        transition must be ascribed to one of these four bit patterns.        Obviously increasing the length of the binary segment will        increase the NLTS identification resolution. A three bit segment        can generate 8 distinct bit patterns, a four bit sequence can        generate 16 bit patterns, and so forth, doubling the resolution        with each additional bit.

A final preliminary step 36 in the NLTS identification process is togenerate estimates for the amount of NLTS shift τ associated with bitpatterns in a binary segment of the length defined at step 34. Forexample, FIG. 7 is a table 74 showing NLTS shift values τ for everypossible bit pattern of a four bit binary segment (d=3). Some NLTS shiftvalues may be estimated values that can be updated and some NLTS shiftvalues may be fixed values. For example, in FIG. 7 the bit pattern 0000may correspond to a fixed amount of NLTS shift τ=A; the bit pattern 0001may initially correspond to an estimated amount of NLTS shift τ=B, andso forth. Initially, the various NLTS shift estimated values need not beparticularly accurate, as they will be adaptively adjusted later in theprocess. The fixed NLTS shift values are based upon known properties ofa particular bit pattern, are assumed to be accurate, and are notadjusted.

Once the discrete-time differentiated ideal step response has beengenerated and NLTS shift estimated and/or fixed values have beendetermined and stored for the various bit patterns that may beencountered in the d+1 bit long segments of a binary sequence, acontinuous-time analog waveform corresponding to a binary sequencewritten to the magnetic head/media channel 14 is received from themagnetic head/media channel 14 at step 38. FIG. 8 shows a sample binarysegment 76 corresponding to a continuous-time analog waveform receivedfrom the magnetic head/media channel 14. The binary segment 76 iscentered around a time k. The binary segment 76 includes the bit b_(k)received at time k, the four bits b_(k−1), b_(k−2), b_(k−3), and b_(k−4)preceding b_(k), and the four bits immediately following b_(k), b_(k+1),b_(k+2), b_(k+3), and b_(k+4). In FIG. 8, the binary segment 76 has thebit pattern 101100001.

The next step 40 in the NLTS identification process is to calculate anestimate n_(k) of the total NLTS error present in a signal received fromthe magnetic head/media channel 14 at a given time k, provided that thebit pattern surrounding k does not correspond to an NLTS fixed value(step 39).

An estimate of the total NLTS error n_(k) for a particular time is basedupon the binary transition that occurs at that particular time as wellas neighboring transitions. In other words, the total NLTS error at aparticular time k is equal to the sum of the NLTS error contributionfrom the transition at time k plus the NLTS error contributions ofseveral neighboring transitions. This phenomenon is best understoodgraphically.

Recall that FIG. 6 shows the discrete-time differentiation 70 of theideal step response for the magnetic head/media channel 14 for a binarytransition occurring at time t=0. FIG. 9 shows the discrete-timedifferentiation of the ideal step response for the magnetic head/mediachannel 14 for a transition occurring at time t=k. The two curves aresubstantially identical except that the curve in FIG. 9 has beentranslated in time and is centered around t=k rather than t=0. FromEquation [2] the NLTS error due to the transition at time k is given byDTS(t)=dts(t)·τIn the discrete time domain Equation [2] may be restated asDTS _(i) =dts _(i) ·τWhere i is a sampling index identifying the various data points 80, 82,. . . 96 of the discrete time differentiation of the ideal step responseof the magnetic head/media channel 14 for a transition at time k. τ is afunction of the bit pattern in a segment of the received binary sequence(b_(k−d), b_(k−d+1), . . . , b_(k)). In the example given earlier, theparameter d was assigned a value d=3. Thus, τ for the transitionoccurring at time k is a function of the bit pattern of the segment ofthe received binary sequence (b_(k−3), b_(k−2), b_(k−1), b_(k)).Referring to FIG. 8, τ(b_(k−3), b_(k−2), b_(k−1), b_(k))=τ(0110).Referring to the table in FIG. 7, τ(0110) corresponds to an NLTS shiftτ(0110)=G. The NLTS error caused by the binary transition at time k isapproximately equal to the discrete-time differentiated ideal stepresponse for a binary transition occurring at time k times τ(0110), ordts₈₈·G. Graphically this means multiplying each data point 80, 82 . . .96 of the discrete-time differentiation of the ideal step response forthe binary transition at time k by an amount G. As is quite clear fromFIG. 9, the NLTS shift of the binary transition at time k based on thebit pattern 0110 will cause NLTS error at times other than time k. Forexample, at time k+1 the NLTS of a binary transition at time k willcause NLTS shift error equal to the value 90 of the discrete-timedifferentiated ideal step response at time k+1 times G. Similarly, attime k−1 the NLTS of the binary transition at time k will cause NLTSshift error equal to the discrete-time value 86 of the differentiatedideal step response at k−1 times G.

Just as the NLTS shift incurred by the binary transition at time kcauses residual NLTS error at times other than time k, the NLTS shift ofbinary transitions occurring at times other than time k will similarlycause residual NLTS error at time k. For example, FIG. 10 shows thediscrete-time differentiation of the ideal step response for themagnetic head/media channel 14 for a binary transition occurring at atime k−1. τ for the transition shift occurring at k−1 is a function ofthe bit pattern of the received binary sequence segment (b_(k−4),b_(k−3), b_(k−2), b_(k−1)). Referring to FIG. 8, τ(b_(k−4), b_(k−3),b_(k−2), b_(k−1))=(1011). Referring to the table in FIG. 7, τ(1011)=L.The NLTS error caused by the binary transition at time k−1 isapproximately equal to dts_(i)·τ(1011)=dts_(i)·L. Graphically thiscorresponds to multiplying each discrete value 98, 100, . . . 114 of thediscrete-time differentiated ideal step response of the binarytransition occurring at time k−1 by an amount L. As can be seen in FIG.10, the NLTS shift of the binary transition at time k−1 will generateNLTS error at time k in an amount equal to the discrete value 108 of thediscrete time differentiated ideal step response for the binarytransition occurring at time k−1 times L, or dts₁₀₈·L.

Similarly, FIG. 11 shows the discrete-time differentiation of the idealstep response for the magnetic head/media channel 14 for a binarytransition occurring at time k+1. τ for the transition occurring at k+1is a function of the bit pattern of the received binary sequence segment(b_(k−2), b_(k−1), b_(k), b_(k+1)). Referring to FIG. 8, τ(b_(k−2),b_(k−1), b_(k), b_(k+1))=τ(1100). Referring to the table in FIG. 7,τ(1100)=M. The NLTS error caused by the binary transition at time k+1 isapproximately equal to dts_(i)·τ(1100)=dts_(i)·M. Graphically thiscorresponds to multiplying each discrete value 116, 118, . . . , 130 ofthe discrete-time differentiated ideal step response of the binarytransition occurring at time k+1 by an amount M. As can be seen in FIG.11, the NLTS shift of the binary transition at time k+1 will generateNLTS error at time k in an amount equal to the discrete value 122 of thediscrete-time differentiated ideal step response for the binarytransition occurring at time k+1 times M, or dts₁₂₂·M.

The total NLTS error at time k resulting from the NLTS shift experiencedby the binary transitions occurring at times k−1, k, and k+1 is equal tothe sum of the NLTS error at time k from each transition, orn _(k) =dts ₁₀₈ ˜L+dts ₈₈ ·G+dts ₁₂₂ ·M.

The discrete-time differentiated ideal step response is the same foreach binary transition in the sequence, only translated in time. Thus,the discrete values of discrete-time differentiated step response of atransition at time 0 (FIG. 6) may be applied to the calculation of theNLTS error estimate at other times. A time window may be defined where−M≦i≦+N. The time window may be symmetrical about the time τ=0 such thatN=M and −M≦i≦+M. The estimate of the total NLTS error at a given time kanywhere in the read back waveform may be given by

$\begin{matrix}{n_{k} = {\sum\limits_{i = {- M}}^{+ M}\;{{dts}_{i} \cdot {{\tau_{k - i}\left( {b_{k - i - d},b_{k - i - d + 1},\ldots\mspace{14mu},b_{k - i}} \right)}.}}}} & \lbrack 3\rbrack\end{matrix}$

Returning to the flowchart of FIG. 2, once the NLTS error estimate iscalculated for time k, the next step 42 is to determine the actual NLTSerror e_(k) in the read back waveform. The NLTS error e_(k) may beobtained by subtracting an equalized waveform from a reconstructed idealwaveform created based on the most likely bit sequence corresponding tothe received waveform. The NLTS error e_(k) can be compared to theestimated NLTS error n_(k) to determine the accuracy of the estimate. Adifference function ι_(K) may be defined as

$\begin{matrix}{\delta_{k} = {{e_{k} - n_{k}} = {e_{k} - {\sum\limits_{i = {- M}}^{+ M}\;{{dts}_{i} \cdot {{\tau_{k - i}\left( {b_{k - i - d},b_{k - i - d + 1},\ldots\mspace{14mu},b_{k - i}} \right)}.}}}}}} & \lbrack 4\rbrack\end{matrix}$

Ideally |ι_(K)| will be as small as possible. In other words, theestimated NLTS error n_(K) will be close or equal to the actual NLTSerror e_(k) in the waveform received from the magnetic head/mediachannel 14. Recall that the original values of τ(b₁, b₂, b₃, b₄) in thetable 74 of FIG. 7 were either estimated or fixed values. The estimatedvalues may be adjusted to minimize ι_(K) as indicated at step 46 of theNLTS identification process.

In one embodiment, the value of τ (FIG. 7) may be fixed to apredetermined value(s) for one or more selected binary sequences. Apredetermined value may be based upon one or more known characteristicsof NLTS behavior. For example, the value for τ(0,0,0,0) may be fixedsuch that A=0 (FIG. 7) if it is known that a succession of four bitswithout transition does not cause NLTS for a fifth bit having atransition.

For the values of τ that are adjustable, minimization of ι_(K) may beaccomplished using the least mean squared algorithm. A new function cmay be defined as

$\begin{matrix}{c = {\delta_{k}^{2} = {\left( {e_{k} - n_{k}} \right)^{2} = \left( {e_{k} - {\sum\limits_{i = {- M}}^{N}\;{{dts}_{i} \cdot {\tau_{k - i}\left( {b_{k - i - d},b_{k - i - d + 1},\ldots\mspace{14mu},b_{k - i}} \right)}}}} \right)^{2}}}} & \lbrack 5\rbrack\end{matrix}$

The gradient of C may be calculated as

$\begin{matrix}{\frac{\partial c}{\partial\tau_{k - i}} = {{- 2} \cdot \delta_{k} \cdot {{dts}_{i}.}}} & \lbrack 6\rbrack\end{matrix}$

The identity index of τ_(k−1) is (b_(k−i−d), b_(k−i−d+1), . . . ,b_(k−i)). The time index k-i is the location where the binary transitionwith which τ_(k−i) is associated occurs. The identity index is limitedby [0,2^(d+1)−1]. The NLTS values can be adaptively obtained byτ_(h+1) ^(j)=τ_(j) ^(j)+μ·ι_(k) ·dts _(i); where j=f(b _(k−i−d) ,b_(k−i−d+1) , . . . b _(k−i))  [7]

The variable μ defines the size of an incremental adjustment step, andthe sign of δ_(k) determines the direction of adjustment. The new valuesfor τ_(k−i) (b_(k−i−d), b_(k−i−d+1), . . . , b_(k−i)) are stored in anNLTS value register bank. In other words, the adjustable τ values storedin table 74 of FIG. 7 may be replaced with the adjusted τ values at step488. The adjusted values are communicated to the pre-compensation block26 in the write channel 12 at step 50.

The steps 38-50 of the NLTS identification process in FIG. 2 may berepeated for each binary transition in the received waveform. Over timethe adjusted NLTS estimates become more and more accurate and thedifference ι_(K) between the actual NLTS error e_(k) and the estimatedNLTS error n_(k) becomes smaller and smaller.

The pre-compensation block 26 in the write channel 12 may use the valuesof τ(b_(k−i−d), b_(k−i−d+1), . . . , b_(k−i)) stored in the NLTS valueregister bank to adjust the timing of binary transitions written to thehead/media channel 14. For example, assume the values in table 74 of theFIG. 7 have been adjusted, and the pre-compensation block 26 identifiesthe bit sequence (b_(k−3), b_(k−1), b_(k−1), b_(k))=0100. The estimatedvalue of τ is E. In other words, it is estimated that the binarytransition will be shifted by an amount E (in light of the bit pattern(b_(k−3), b_(k−1), b_(k−1), b_(k))=0100) when it is written to thestorage medium 18. The pre-compensation block 26 may alter the timing ofthe transition at time k by an amount −E. The pre-compensation amount −Ewill combine with the NLTS shift amount E to cancel-out the NLTS shiftand the transition will occur at the proper time k when the transitionis written to the storage medium.

FIG. 12 is a block diagram of a preferred embodiment of a magnetic datastorage device read channel implementing the NLTS identification processdescribed above. User data b_(k) 202 are written to the magnetichead/media channel 204. The magnetic head/media channel 204 ischaracterized by the transfer function H(jω). White gaussian systemnoise is added at 206. The read channel 20 includes automatic gaincontrol (AGC) 208; a continuous time filter (CTF) 210; ananalog-to-digital converter (ADC) 212; and a finite impulse responsefilter (FIR) 214. The output of the FIR filter 214 is input to a Viterbidetector (VTB) 216, and a delay line 220. The VTB detector 216 outputs abinary signal {circumflex over (b)}_(k) which is a high reliabilityestimate of the original user data signal b_(k) 202 written to themagnetic head/media channel 204. The output {circumflex over (b)}_(k) ofthe VTB detector 216 is input to a reconstruction filter 218 and an NLTSidentity index module 224. The NLTS identity index module 224 identifiesthe bit patterns of finite segments of binary sequence {circumflex over(b)}_(k) output from the VTB detector 216. The reconstruction filter 218generates the ideal waveform ŷ_(k) from the binary sequence {circumflexover (b)}_(k) based on the target polynomial of the read channel. Theideal waveform ŷ_(k) is subtracted from the output of the FIR filter 214y_(k) at summing junction 222. The output of the FIR filter 214, isdelayed by delay line 220 in order to maintain synchronization with theoutput of the reconstruction filter 218. The difference between y_(k)and ŷ_(k) provides the error signal e_(k).

The target polynomial dst(t) is provided at 226 and the discrete-timedifferentiation of the target (ideal) step response is calculated at228. The discrete-time differentiation of the target step responsedts_(i) is provided to an NLTS error estimation module 230, and an NLTSidentification module 236. When a waveform is received from the magnetichead/media channel 204, and the VTB detector 216 outputs the most likelybinary sequence {circumflex over (b)}_(k) corresponding to the receivedwaveform, the NLTS identity index module 224 identifies the bit patternin each successive segment of the binary sequence. The length of the bitpatterns identified by the NLTS identify index module 224 is determinedby the value of the parameter d. The binary segment length being equalto d+1. The bit patterns identified by the NLTS identity index module224 are used to identify values for the NLTS shift estimate. Each valueof the NLTS shift estimate τ is a function of the preceding bit pattern(τ_(k−i) (b_(k−i−d), b_(k−i−d+1), . . . , b_(k−i))). An NLTS valueregister bank 232 identifies the appropriate value of τ for eachsuccessive binary segment. The τ values are provided to the NLTSestimation module 230, as well as to the pre-compensation circuitry 238in the write channel. The τ values provided to the NLTS error estimationmodule 230 are used to calculate the NLTS error estimate n_(k) for thebinary transitions in the received waveform. The NLTS estimate n_(k) issubtracted from the error signal e_(k) at summing junction 234 toproduce the difference signal ι_(k). ι_(k) is provided to the NLTSidentification module 236 along with the discrete-time differentiationof the target step response 228. The NLTS identification module 236adjusts the values of τ as described above in an effort to reduce themagnitude of ι_(k). The adjusted values of i are then stored in the NLTSvalue register bank 232, replacing the previous estimates correspondingto the various bit patterns generated by the binary segments of lengthd+1. Thus, the NLTS values that are not fixed are continually refined,and improved NLTS values are provided to the pre-compensation circuitry238 so that the write channel can compensate for expected NLTS shiftwhen it writes data to the magnetic head/media channel 14.

In various embodiments, two or more of the modules and/or blocks shownin FIG. 12 or discussed herein may be physically and/or functionallycombined. Any one or combination of modules and/or blocks may bereferred to in general as an NLTS module. Module is not to be regardedas a limiting term but rather as a term encompassing any type of device,circuit, component, or element to perform at least the functiondiscussed in relation thereto.

Referring now to FIGS. 13A-13G, various exemplary implementations of thepresent invention are shown. Referring now to FIG. 13A, the presentinvention can be implemented in a hard disk drive 400. In someimplementations, the signal processing and/or control circuit 402 and/orother circuits (not shown) in the HDD 400 may process data, performcoding and/or encryption, perform calculations, and/or format data thatis output to and/or received from a magnetic storage medium 406.

The HDD 400 may communicate with a host device (not shown) such as acomputer, mobile computing devices such as personal digital assistants,cellular phones, media or MP3 players and the like, and/or other devicesvia one or more wired or wireless communication links 408. The HDD 400may be connected to memory 409 such as random access memory (RAM), lowlatency nonvolatile memory such as flash memory, read only memory (ROM)and/or other suitable electronic data storage.

Referring now to FIG. 13B, the present invention can be implemented in adigital versatile disc (DVD) drive 410. For example, the presentinvention may be implemented on a mass data storage device of the DVDdrive 410. The signal processing and/or control circuit 412 and/or othercircuits (not shown) in the DVD 410 may process data, perform codingand/or encryption, perform calculations, and/or format data that is readfrom and/or data written to an optical storage medium 416. In someimplementations, the signal processing and/or control circuit 412 and/orother circuits (not shown) in the DVD 410 can also perform otherfunctions such as encoding and/or decoding and/or any other signalprocessing functions associated with a DVD drive.

The DVD drive 410 may communicate with an output device (not shown) suchas a computer, television or other device via one or more wired orwireless communication links 417. The DVD 410 may communicate with themass data storage 418, which stores data in a nonvolatile manner. Themass data storage 418 may include a hard disk drive (HDD). The HDD mayhave the configuration shown in FIG. 13A. The HDD may be a mini HDD thatincludes one or more platters having a diameter that is smaller thanapproximately 1.8″The DVD 410 may be connected to memory 419 such asRAM, ROM, low latency nonvolatile memory such as flash memory and/orother suitable electronic data storage.

Referring now to FIG. 13C, the present invention can be implemented in ahigh definition television (HDTV) 420. For example, the invention may beimplemented on a mass data storage of the HDTV 420. The HDTV 420receives HDTV input signals in either a wired or wireless format andgenerates HDTV output signals for a display 426. In someimplementations, signal processing circuit and/or control circuit 422and/or other circuits (not shown) of the HDTV 420 may process data,perform coding and/or encryption, perform calculations, format dataand/or perform any other type of HDTV processing that may be required.

The HDTV 420 may communicate with the mass data storage 427 that storesdata in a nonvolatile manner such as on a magnetic storage devices. Atleast one HDD may have the configuration shown in FIG. 13A and/or atleast one DVD may have the configuration shown in FIG. 13B. The HDD maybe a mini HDD that includes one or more platters having a diameter thatis smaller than approximately 1.8″. The HDTV 420 may be connected tomemory 428 such as RAM, ROM, low latency nonvolatile memory such asflash memory and/or other suitable electronic data storage. The HDTV 420also may support connections with a WLAN via a WLAN network interface429.

Referring now to FIG. 13D, the present invention may be implemented in amass data storage device of a vehicle control system. In someimplementations, a powertrain control system 432 receives inputs fromone or more sensors such as temperature sensors, pressure sensors,rotational sensors, airflow sensors and/or any other suitable sensorsand/or that generates one or more output control signals such as engineoperating parameters, transmission operating parameters, and/or othercontrol signals.

The present invention may also be implemented in relation to othercontrol systems 440 of the vehicle 430. For example, the control system440 may likewise receive signals from input sensors 442 and/or outputcontrol signals to one or more output devices 444. In someimplementations, the control system 440 may be part of an anti-lockbraking system (ABS), a navigation system, a telematics system, avehicle telematics system, a lane departure system, an adaptive cruisecontrol system, a vehicle entertainment system such as a stereo, DVD,compact disc and the like. Still other implementations are contemplated.

The powertrain control system 432 may communicate with mass data storage446 that stores data in a nonvolatile manner. The mass data storage 446may include magnetic storage devices such as hard disk drives HDD. Atleast one HDD may have the configuration shown in FIG. 13A and/or atleast one DVD may have the configuration shown in FIG. 13B. The HDD maybe a mini HDD that includes one or more platters having a diameter thatis smaller than approximately 1.8″. The powertrain control system 432may be connected to memory 447 such as RAM, ROM, low latency nonvolatilememory such as flash memory and/or other suitable electronic datastorage. The powertrain control system 432 also may support connectionswith a WLAN via a WLAN network interface 448. The control system 440 mayalso include mass data storage, memory and/or a WLAN interface (all notshown).

Referring now to FIG. 13E, the present invention can be implemented in acellular phone 450 that may include a cellular antenna 451. The presentinvention may be implemented in the mass data storage of the cellularphone 450. In some implementations, the cellular phone 450 includes amicrophone 456, an audio output 458 such as a speaker and/or audiooutput jack, a display 460 and/or an input device 462 such as a keypad,pointing device, voice actuation and/or other input device. The signalprocessing and/or control circuits 452 and/or other circuits (not shown)in the cellular phone 450 may process data, perform coding and/orencryption, perform calculations, format data and/or perform othercellular phone functions.

The cellular phone 450 may communicate with mass data storage 464 thatstores data in a nonvolatile manner on magnetic storage devices such ashard disk drives HDD. At least one HDD may have the configuration shownin FIG. 13A. The HDD may be a mini HDD that includes one or moreplatters having a diameter that is smaller than approximately 1.8″. Thecellular phone 450 may be connected to memory 466 such as RAM, ROM, lowlatency nonvolatile memory such as flash memory and/or other suitableelectronic data storage. The cellular phone 450 also may supportconnections with a WLAN via a WLAN network interface 468.

Referring now to FIG. 13F, the present invention can be implemented in aset top box 480. The present invention be implemented in the mass datastorage of the set top box 480. The set top box 480 receives signalsfrom a source such as a broadband source and outputs standard and/orhigh definition audio/video signals suitable for a display 488 such as atelevision and/or monitor and/or other video and/or audio outputdevices. The signal processing and/or control circuits 484 and/or othercircuits (not shown) of the set top box 480 may process data, performcoding and/or encryption, perform calculations, format data and/orperform any other set top box function.

The set top box 480 may communicate with the mass data storage 490 thatstores data in a nonvolatile manner. The mass data storage 490 mayinclude magnetic storage devices for example hard disk drives HDD. Atleast one HDD may have the configuration shown in FIG. 13A. The HDD maybe a mini HDD that includes one or more platters having a diameter thatis smaller than approximately 1.8″. The set top box 480 may be connectedto memory 494 such as RAM, ROM, low latency nonvolatile memory such asflash memory and/or other suitable electronic data storage. The set topbox 480 also may support connections with a WLAN via a WLAN networkinterface 496.

Referring now to FIG. 13G, the present invention can be implemented in amedia player 500. The present invention may be implemented in a massdata storage of the media player 500. In some implementations, the mediaplayer 500 includes a display 507 and/or a user input 508 such as akeypad, touchpad and the like. In some implementations, the media player500 may employ a graphical user interface (GUI) that typically employsmenus, drop down menus, icons and/or a point-and-click interface via thedisplay 507 and/or user input 508. The media player 500 further includesan audio output 509 such as a speaker and/or audio output jack. Thesignal processing and/or control circuits 504 and/or other circuits (notshown) of the media player 500 may process data, perform coding and/orencryption, perform calculations, format data and/or perform any othermedia player function.

The media player 500 may communicate with mass data storage 510 thatstores data such as compressed audio and/or video content in anonvolatile manner. In some implementations, the compressed audio filesinclude files that are compliant with MP3 format or other suitablecompressed audio and/or video formats. The mass data storage may includemagnetic storage devices for example hard disk drives HDD. At least oneHDD may have the configuration shown in FIG. 13A. The HDD may be a miniHDD that includes one or more platters having a diameter that is smallerthan approximately 1.8″. The media player 500 may be connected to memory514 such as RAM, ROM, low latency nonvolatile memory such as flashmemory and/or other suitable electronic data storage. The media player500 also may support connections with a WLAN via a WLAN networkinterface 516.

It is intended that the foregoing detailed description be understood asan illustration of selected forms that the invention can take and not asa definition of the invention. It is only the following claims,including all equivalents, that are intended to define the scope of thisinvention.

1. A magnetic media data storage system comprising: a write head towrite data to a magnetic medium; a read head to read the data from themagnetic medium and to generate a waveform; a Non-Linear TransitionShift (NLTS) module adapted to compensate for NLTS in the waveform usingan adjustable NLTS estimate value, determine an NLTS error in a writetime of a binary transition from the waveform after compensating forNLTS, and adjust the NLTS estimate value based at least in part on theNLTS error.
 2. The magnetic media data storage system of claim 1,wherein the NLTS module is further adapted to identify NLTS in thewaveform, associate the NLTS with a specific pattern in the data, andadjust the NLTS estimate value.
 3. The magnetic media data storagesystem of claim 1, further comprising a compensation circuit adapted toadjust a time at which a transition corresponding to a specific patternin the data is written to the write head based on the NLTS estimatevalue.
 4. The magnetic media data storage system of claim 3, wherein theNLTS module and compensation circuit are together adapted to adjust thetime at which the binary transition is written to the write head basedon either the NLTS estimate value or a NLTS fixed value.
 5. The magneticmedia data storage system of claim 1, wherein the NLTS module determinesthe NLTS error based on a discrete-time differentiation of a readchannel target step response of a binary transition and a non-lineartransition shift value for a binary transition shift.
 6. The magneticmedia data storage device of claim 1, wherein the NLTS module is adaptedto adjust the NLTS error estimate based upon a comparison between theNLTS error estimate and a NLTS actual error.
 7. The magnetic datastorage system of claim 6 comprising a read channel adapted to determinethe NLTS actual error.
 8. The magnetic media data storage system ofclaim 1, wherein the NLTS module further includes a NLTS value registerto store the NLTS estimate value.
 9. The magnetic media data storagesystem of claim 1, further comprising a read channel having: ananalog-to-digital converter configured to convert an analog signal,obtained from the magnetic medium, into a digital signal; a finiteimpulse response filter configured to receive the digital signal andoutput a filtered digital signal; a viterbi detector to generate anestimate of an original data signal written to the write head; areconstruction filter to generate an equalized data signal estimatebased upon the estimate of the original data signal and a targettransfer characteristic of the read channel; and a summing junction tocompare the filtered digital signal to the equalized data signalestimate and to output an actual error signal.
 10. The magnetic mediadata storage system of claim 1 comprising a NLTS error estimation moduleadapted to generate the NLTS error estimate value based on adiscrete-time differentiation of a target step response and a pluralityof NLTS corresponding to a plurality of specific data patterns.
 11. Amethod comprising: generating a waveform based on data read from amagnetic medium; compensating for NLTS using an adjustable NLTS estimatevalue; determining an NLTS error in a write time of a binary transitionfrom the waveform after compensating for the NLTS; and adjusting theNLTS estimate value based at least in part on the NLTS error.
 12. Themethod of claim 11 further comprising: identifying the NLTS in thewaveform; associating the NLTS with a specific pattern in the data; andadjusting the NLTS estimate value.
 13. The method of claim 11, whereincompensating for the NLTS further comprises adjusting a time at which atransition corresponding to a specific pattern is written to a writehead based on the NLTS estimate value.
 14. The method of claim 13comprising adjusting the time at which the transition is written basedon either the NLTS estimate value or a NLTS fixed value.
 15. The methodof claim 11 comprising adjusting the NLTS estimate value based on acomparison between the NLTS estimate value and an NLTS actual error. 16.The method of claim 11 comprising storing the NLTS estimate value inmemory.
 17. The method of claim 11 comprising: converting an analogsignal, obtained from the magnetic medium, into a digital signal;receiving the digital signal and outputting a filtered digital signal;generating an estimate of an original data signal written to the writehead; generating an equalized data signal estimate based upon theestimate of the original data signal and a target transfercharacteristic of a read channel; and comparing the filtered digitalsignal to the equalized data signal estimate; and outputting an actualerror signal.
 18. The method of claim 11 comprising generating the NLTSerror estimate based on a discrete-time differentiation of a target stepresponse and a plurality of NLTS corresponding to a plurality ofspecific data patterns.
 19. The method of claim 11 comprisingdetermining the NLTS error based on a discrete-time differentiation of aread channel target step response of a binary transition and anon-linear transition shift value for a binary transition shift.